The thalamic lateral geniculate nucleus (LGN) is found in the primary neural pathway between the eye and visual cortex, and it controls the flow of visual information to the brain in large measure through the influence of specific nuclei in the brainstem. Pathways from the brainstem can powerfully effect the LGN and are believed to reflect behavioral states, such as arousal or attention and the occurrence of eye movements. HOwever, the anatomy and physiology of these brainstem circuits are not well understood. This research will provide a comprehensive, multi-disciplinary description of the structural and functional influences of the brainstem on the LGN. In doing so, these studies will elucidate, more generally, the role of the thalamus in relaying sensory information to the e cortex, and they will aid in understanding the role of a key neural element underlying vision. Aims 1 and 3 are to demonstrate the effects of electrical and chemical activation of individual brainstem nuclei on the extra- and intracellular responses of LGN cells to visual stimuli. Aims 2 and 4 are to describe, at the light and electron microscopic level by means of retrograde and anterograde tracers, the morphology and ultrastructure of brainstem neurons that project to the LGN and other thalamic nuclei. Aim 5 is to confirm and describe key thalamic pathways through which the brainstem indirectly controls the LGN.